The trio of archaeologists and helpers sat in a rectangular patch of dirt, scratching at the ground with hoes and trowels, shooing the dirt into dust pans which they delivered into plastic buckets. A small white tent rustled in the Presidio parade ground’s jolting winds, just 75 yards from the historic officer’s quarters, San Francisco’s oldest, or second-oldest existing building, depending on who you ask.

“The first 70 years of people living here is quite a bit of a mystery,” said Presidio archaeologist Kari Jones, who is leading the excavation.

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Despite its status as one of San Francisco’s two oldest neighborhoods (there is debate whether Mission Dolores is older), the Presidio still clutches tightly to its secrets. And that is why Jones and archaeologists are digging: to try and find the remnants of the wall that marked the western edge of the original Spanish fortress.

If the team can find the wall, it will provide the pivotal waypoint to identifying the fortress’s layout, a network of adobe buildings that once housed the Presidio’s original Spanish soldiers and their families.

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The team recently kicked off the dig, but they expect it to take decades to complete.

“We’re patient,” Jones said, “because we know over time, all these small finds accumulate into bigger, richer, larger portraits of life.”

The search for the wall has turned up tiny bits of early Presidio life. The soil excavated from the site is sifted, yielding archaeological prizes such as pieces of terra cotta roof tiles, ceramics, coins and animal bones. The finds are cataloged and stored in the shelves of a special room kept at bone-chilling temperatures.

Jones said it is likely many of the earliest settlers to settle the Presidio in 1776 were illiterate, resulting in scant records and history. So the bits and pieces pulled from the soil make up the footnotes in the story of those early inhabitants who came to the land, which was already occupied by Ohlone Indians.

“We are currently writing the history books with our trowels,” Jones said.